4.3 To analyse the structure of the earth and to measure movements  (Page 4/3)

Natural sciences

Planet earth and the universe

The earth

Educator section

Memorandum

Assignment 1:

• Assess using the assessment matrix.

Assignment 2:

Main Ideas

• Earthquake: evening of 29 September 1969.
• Registers 6.5 on the Richter Scale.
• Chaos in most places.
• Rumbling grew louder and louder and was followed by tremendous quake.
• The whole earth shuddered and people ran about panic stricken.
• Rescuers used the Post Office as a base because it was the only place which had electricity.
• Homes were badly damaged and people were badly injured.
• Emergency aid streamed to the disaster towns and the police and army co-operated.
• People were housed in tents and field hospitals were erected.
• The water shortage was alleviated and food was supplied.
• R13 million donated by the Disaster Committee

Assignment 3:

• (sketch)

Assignment 4:

1. The Richter Scale is the instrument (scale) which seismologists use to measure the strength of an earthquake.

2. Seismologists are scientists who study earthquakes.

3. The place at which the shock waves first reach the surface of the earth is known as the epicentre.

4. If the pressure in the mantel under the crust builds up then magma is forced through weak places and cracks. These weak places then form volcanic pipes.

5. Active volcanoes are volcanoes which erupt from time to time.

Leaner section

Content

Activity: to analyse the structure of the earth and to measure movements in it (natural disasters) [lo 2.1, lo 2.3]

STRUCTURE OF THE EARTH

• Scientists believe that Earth came into existence about 4 600 million years ago as a large cloud of gas and dust swirling around in space. While it was rotating it shrank to an extremely hot, liquid ball. The surface gradually cooled and a crust of solid rock formed which weathered to the mountains, soil and sand on which we live today.
• Earth is continually changing. The land masses (continents) are not only moving, but new crust is forming all the time. The movement of the crust is called continental drift and it is still occurring. America, for example, is moving gradually away from Europe. This movement has already led to telephone cables under the Atlantic breaking.

FOUR LAYERS OF THE EARTH

• The Crust

The crust is the outermost layer and has a thickness of from 5 km to 70 km. Under the oceans the crust can be as thin as 5 km and where there are mountains the crust can be as thick as 70 km. Beneath the crust there are three other layers. They are:

• The Mantle

The mantle is 2 900 km thick. It is solid but contains slowly flowing currents of semi-melted metals.

• The outer Core

The outer core consists of liquid metal and is responsible for the earth’s magnetic field. It is 2 240 km thick.

• The inner Core

The inner core in the middle of the earth is probably solid and consists mainly of metals. The temperature is 3 700 degrees Celsius. Water boils at 100 degrees Celsius. The inner core has a diameter of 2 240 km.

The lava that flows from volcanoes comes from the mantle.

TASK 1: GROUP WORK

Use playing dough (four different colours) to make a model of Earth’s structure. The thickness of each layer should be more or less proportional to the actual thickness of the earth’s layer.